The present invention relates to a fuse for submunitions of the type which are carried by a projectile and are expelled from this to fall on the target.
Such sub-munitions are normally disposed within a suitable container housed in a projectile which is provided with an expulsion charge which is activated at a determined point of the trajectory of the projectile itself in such a way as to expel the sub-munitions; each of these, in the first part of the trajectory which starts after their expulsion, is given the same movement as has been imparted to the projectile and therefore, if this is constituted by a shell fired from a gun of conventional type, each sub-munition as well as following a predetermined trajectory, is also provided with a rotary motion substantially about its longitudinal axis.
The fuses of sub-munitions of the type indicated are normally provided with an arming device comprising a striker member movable substantially in the direction of its longtiudinal axis and a detonator carried by a slide movable from a first position, in which the said detonator is located out of the path of the striker member to a second position in which the detonator is, on the other hand, carried into the path of the member itself and beneath this. The striker member is movable from a first position in which it prevents the displacement of the said slide, to a second position in which it allows the displacement of the slide itself; for the purpose of generating the axial displacement of the striker member from the first to the second position first noted, this is normally provided with a threaded stem screwed into a corresponding threaded hole of a small bush movable axially within the body of the fuse, in such a way that the striker member can be brought from the first to the second position first defined following unscrewing of the threaded stem from the corresponding threaded hole. When the striker member is located in this second position the slide is displaced by the action of a spring from the first to the second position first defined and therefore the fuse is in its armed configuration in which the striker member is above the detonator and controls the explosion of the associated charge when, because of the striking of the sub-munition on the ground, the inertial force of the striker member itself thrusts this against the detonator.
In fuses of the type described, at the upper end of the striker member there is normally connected a flexible element of annular form which is normally folded in a pack above the fuse when the associated sub-munition is located within the projectile and which disposes itself in an open configuration because of the aerodynamic forces which act on it after the sub-munition has been ejected from the projectile. Since the sub-munition is given a rotary motion, and because of the aerodynamic resistance generated by the said flexible element, this latter tends to oppose the rotation of the sub-munition in this way giving rise to a moment on the striker member to which the flexible element is connected; the said moment generates a rotation of the striker member with respect to the body of the fuse, and therefore causes the unscrewing of the striker member itself from the corresponding threaded hole first mentioned, in such a way as to bring the striker member from the first position to the second position previously described.
Fuses of the type described have the disadvantage of not causing explosion of the detonator when the sub-munitions on which they are mounted fall on soft ground, for example snow covered ground, or reach the ground with a trajectory which forms a small angle therewith. In this case the sub-munitions lying on the ground can explode when struck inadvertently, in this way acting as a land mine which could cause serious danger to those who have themselves fires the sub-munitions.
There are known fuses which are fitted with devices operable to cause explosion of the associated sub-munitions a predetermined time after they have fallen on the ground; such devices comprise a striker member operable to come into contact with the detonator, the displacement of which is controlled by an assembly of mechanical members normally actuated by springs, in which there are provided delay means operable to allow the said displacement after a certain time from its activation.
Such devices have the disadvantage of being very complex overall and of low reliability; in fact, the members of the assembly first mentioned must be made with very strict tolerances and require delicate operations for their assembly, moreover, the operation of the delay means, normally based on the transfer of a suitable viscus fluid, is considerably influenced by the ambient conditions and is not reliable.